This means you can only use the jump-start ability one time
With cards like Kruphix, God of HorizonsKruphix, God of Horizons, Inga and EsikaInga and Esika, Xolatoyac, the Smiling FloodXolatoyac, the Smiling Flood, and others, you can spend a lot of mana on other players' end steps to ensure they don't have as many opportunities to disrupt your game plan and to allow you to keep your own disruption spells castable at a moment's notice
You wont be disappointed to open one in your pack, but its not the big hits youre really hoping for
And your creatures still have their abilities, so you can exile Akroma and get a 4/4 flying, haste, vigilance, pro-Red, pro-Black, trample Angel Zombie and swing, or that annoying indestructible creature you just countered, well, get a 4/4 indestructible Zombie
That said, you do have the potential to cast this spell for as cheap as just three blue mana, which is cheaper than most extra turn spells, and those generally have a downside